If they want to avoid another hung parliament, both sides need to take more risks. This isn't a time for small-ball politics.

David Cameron and Ed Miliband look on during the service to celebrate the 60th anniversary of the Coronation of Queen Elizabeth II at Westminster Abbey in London. Photograph: Getty Images.

To win a majority at the next election, both Labour and the Conservatives will need to defy recent history. No governing party has increased its share of the vote since 1974; no opposition has achieved an overall victory at the first attempt for more than 80 years. Faced with these odds, each side is already preparing for another hung parliament.

One shadow minister recently told me that he had been encouraged to look for “points of agreement” with the Lib Dems and to consider constitutional reforms that would appeal to the party, citing the example of proportional representation for local elections. In the Tories’ case, David Cameron is privately discussing plans to offer his MPs a vote on a second power-sharing agreement. Impressed by the discipline of Clegg’s backbenchers compared with that of his truculent troops, Cameron wants his party’s hands “dipped in blood”. Hoping for a win but preparing for a draw, it is Antonio Gramsci’s maxim of “pessimism of the intellect, optimism of the will” that is guiding both sides.

Yet in an age of voter promiscuity, it remains conceivable that either party could gain a decisive advantage before 2015. The common concern among Labour and Tory MPs is that their leaders are failing to grasp the opportunity to do so. In Ed Miliband’s party, there is increasing anxiety at the disparity between the boldness of his rhetoric and the timidity of his policy proposals. This has led Andy Burnham to break ranks and publicly challenge Miliband to back his plan for an integrated national health and care service. In an earlier and similarly unauthorised intervention, he called for the party to pledge to ban zero-hours contracts.

Privately, Miliband’s allies are dismissive of such intemperance. To a degree under-appreciated in Westminster, the Labour leader’s strategy has been shaped by the constitutional novelty of a fixed-term parliament. As one shadow cabinet member put it to me, “We know the date of the next election. There’s no danger of the government cutting and running . . . So we can work backwards. We know when we need our pledge cards by, our manifesto by and our party candidates selected by.” The reasons given for Labour not showing its hand too early are both familiar and persuasive: that the best policies are stolen and the party is lumbered with the worst. In addition, Ed Balls, who is charged with restoring Labour’s economic credibility, is determined to postpone major spending commitments until the state of the public finances is clearer.

That the opposition’s MPs know and understand all of this does little to assuage their disquiet. One comparison made with increasing frequency is with Miliband’s erstwhile mentor Gordon Brown, who similarly offered periodic hints of a social-democratic master plan, only for the cupboard to prove bare when he arrived in Downing Street.

To this, those close to the Labour leader reply: “Watch this space.” The first phase of the party’s policy review has been completed and the fruits will begin to emerge at this autumn’s conference. Labour has spent the summer charting how the “cost of living” has surged under the coalition, but if the party is to win in 2015 it won’t be enough to convince voters that they’re worse off under the Tories. It will also need to convince them they’d be better off under Labour. The aim of Miliband’s speech will be to bridge this gap, with energy and housing two of the candidates for major policy announcements.

Having offered a radical diagnosis of Britain’s problems, the onus is on the Labour leader to provide radical prescriptions. A pledge to build a million affordable homes, to introduce universal childcare for preschool children and to renationalise the railways all fall into this category. At some stage, this will require Miliband to abandon his reticence and make an open case for borrowing to invest. As long as the Tories are able to accuse Labour of wanting to spend more – and with the opposition unwilling or unable to explain why – the party will struggle to shift the terms of debate in its favour.

The Conservatives are fond of deriding Labour’s alleged “35 per cent strategy”, under which a coalition of the party’s core supporters and Lib Dem defectors allow it to crawl over the electoral finish line – but few note the irony that the Tory leadership has now adopted its own version of this game plan. Under heavy fire from the Ukip insurgency, the party has retreated to its core territory of welfare, immigration and Europe.

While this might be enough to preserve the Tories’ status as the single largest party, it will not win them the majority they crave. To achieve an overall victory, the party needs to expand its appeal considerably among those groups that have shunned it at the past four elections: ethnic minorities, northerners, Scots and LGBT voters. With the exception of equal marriage, few visible efforts have been made to do so. In January of this year, Tory strategists briefed that Cameron was so concerned at how the issue of race was damaging support for the party that he would address it “head-on with a speech in the next two months”. Yet seven months on, nothing has been heard. Instead, the party has further damaged its reputation with ethnic minorities through a series of demagogic stunts on immigration.

Where both the Conservatives and Labour agree is that Britain faces greater problems than at any time since 1979. The long-assumed link between a market economy and rising living standards has been severed and the country’s prosperity has been permanently dented by the financial crisis. Yet neither side has so far offered a persuasive account of how it would govern after 2015. Both proceed with caution as if afraid to reveal their true intentions to voters. But if they want big rewards, they will eventually need to take big risks.